INVITED REVIEW POLYMERIC DELIVERY SYSTEMS FOR CONTROLLED DRUG RELEASE

"Bamboo-like" strong and tough sodium alginate/polyacrylate hydrogel fiber with directional controlled release for wound healing promotion

Skin, as the biggest organ and outermost surface of the human body, is prone to injury due to various challenges, especially the expanding potential of accidents, which bring a huge social and economic burden. Hydrogels are emerging as the most promising candidate for wound dressings, which not only fulfill the varied requirements of dressings but also serve as drug carriers. But limited breathability, rapid drug release, and inadequate mechanical properties remains a significant challenge. Herein, we report a strong and tough sodium alginate/polyacrylate hydrogel fibers-based dressing with directional controlled drug release for wound healing promotion. Mimicking the bamboo structure, the drug solution is encapsulated within the fiber, and the rate of drug release can be modulated by controlling the wall thickness of the fiber. A cross-network structure in the hydrogel fiber through hydrogen bond and calcium ion crosslinking resulted in a 38 % increase in tensile strength. By precisely controlling the feeding process during weaving, drug-loaded fibers can be prepared at specific locations to facilitate targeted delivery to skin wound sites. Drug-loaded fabric has the breathability and biocompatibility required for dressings to promote wound healing. The findings highlight the potential of alginate/polyacrylate hydrogel fabrics for effective wound treatment.

Unveiling the multifaceted potential of amyloid fibrils: from pathogenic myths to biotechnological marvels

Amyloid fibrils, historically stigmatized due to their association with diseases like Alzheimer's and Parkinson's, are now recognized as a distinct class of functional proteins with extraordinary potential. These highly ordered, cross-β-sheet protein aggregates are found across all domains of life, playing crucial physiological roles. In bacteria, functional amyloids like curli fibers are essential for surface adhesion, biofilm formation, and viral DNA packaging. Fungal prions exploit amyloid conformations to regulate translation, metabolism, and virulence, while mammalian amyloids are integral to melanin synthesis, hormone storage, and antimicrobial defense. The stability and hydrophobic nature of amyloid scaffolds underpin these diverse biological functions. Beyond their natural roles, amyloid fibrils offer unique capabilities in biomedicine, nanotechnology, and materials science. Their exceptional mechanical strength and biocompatibility make them ideal for controlled drug delivery, tissue engineering scaffolds, and enzyme immobilization. The intrinsic fluorescence and optical properties of certain amyloids open up innovative applications in biosensors, molecular probes, and optoelectronic devices. Furthermore, amyloid fibrils can template metal nanowires, enhance conducting materials, and form nanocomposites by integrating with polymers. This newfound appreciation for the functional diversity of amyloids has ignited intense research efforts to elucidate their molecular mechanisms, stability, and tunable properties. By unraveling the structural intricacies of functional amyloids, researchers aim to harness their remarkable attributes for groundbreaking biomedical therapies, advanced nanomaterials, and sustainable biotechnological innovations. This review explores the transformative journey of amyloids from pathological entities to biotechnological marvels, highlighting their vast potential across agriculture, environmental remediation, and industrial processes.

pH factors in chronic wound and pH-responsive polysaccharide-based hydrogel dressings

Chronic wounds present a significant healthcare challenge marked by complexities such as persistent bleeding, inhibited cell proliferation, dysregulated inflammation, vulnerability to infection, and compromised tissue remodeling. Conventional wound dressings often prove inadequate in addressing the intricate requirements of chronic wound healing, leading to slow healing and heightened susceptibility to infections in patients with prolonged medical conditions. Bacterial biofilms in chronic wounds pose an additional challenge due to drug resistance. Advanced wound dressings have emerged as promising tools in expediting the healing process. Among these, pH-responsive polysaccharide-based hydrogels exhibit immense prospect by adapting their functions to dynamic wound conditions. Despite their potential, the current literature lacks a thorough review of these wound dressings. This review bridges this gap by meticulously examining factors related to chronic wounds, current strategies for healing, and the mechanisms and potential applications of pH-responsive hydrogel wound dressings as an emerging therapeutic solution. Special focus is given to their remarkable antibacterial properties and significant self-healing abilities. It further explores the pH-monitoring functions of these dressings, elucidating the associated pH indicators. This synthesis of knowledge aims to guide future research and development in the field of pH-responsive wound dressings, providing valuable insights into their potential applications in wound care.

Synthesis and Photochemical Uncaging of Alkene-Protected, Polymer-Bound Vicinal Frustrated Lewis Pairs

Polymeric materials bearing Frustrated Lewis Pair (FLP) functionality are promising candidates for use as heterogeneous catalysts and adaptive materials, but synthetic access to FLP-functional polymers remains limited due to the incompatibility of FLPs with standard polymerization chemistries. Herein, we describe a synthetic approach that "cages" highly reactive vicinal phosphine-borane FLPs as covalent alkene adducts, which are stable to Ni-mediated vinyl addition polymerization. We discovered that the caged FLP adducts can be photochemically activated to liberate vicinal FLPs, enabling spatiotemporally controlled release of FLPs from polymeric precursors.

Engineered Hierarchical Microdevices Enable Pre-Programmed Controlled Release for Postsurgical and Unresectable Cancer Treatment

Drug treatment is required for both resectable and unresectable cancers to strive for any meaningful improvement in patient outcomes. However, the clinical benefit of receiving conventional systemic administrations is often less than satisfactory. Drug delivery systems are preferable substitutes but still fail to meet diverse clinical demands due to the difficulty in programming drug release profiles. Herein, a microfabrication concept, termed "Hierarchical Multiple Polymers Immobilization" (HMPI), is introduced and biodegradable-polymer-based hierarchical microdevices (HMDs) that can pre-program any desired controlled release profiles are engineered. Based on the first-line medication of pancreatic and breast cancer, controlled release of single gemcitabine and the doxorubicin/paclitaxel combination in situ for multiple courses is implemented, respectively. Preclinical models of postsurgical pancreatic, postsurgical breast, and unresectable breast cancer are established, and the designed HMDs are demonstrated as well-tolerable and effective treatments for inhibiting tumor growth, recurrence, and metastasis. The proposed HMPI strategy allows the creation of tailorable and high-resolution hierarchical microstructures for pre-programming controlled release according to clinical medication schedules, which may provide promising alternative treatments for postsurgical and unresectable tumor control.

Ferrocene-Based Drugs, Delivery Nanomaterials and Fenton Mechanism: State of the Art, Recent Developments and Prospects

Ferrocene has been the most used organometallic moiety introduced in organic and bioinorganic drugs to cure cancers and various other diseases. Following several pioneering studies, two real breakthroughs occurred in 1996 and 1997. In 1996, Jaouen et al. reported ferrocifens, ferrocene analogs of tamoxifen, the chemotherapeutic for hormone-dependent breast cancer. Several ferrocifens are now in preclinical evaluation. Independently, in 1997, ferroquine, an analog of the antimalarial drug chloroquine upon the introduction of a ferrocenyl substituent in the carbon chain, was reported by the Biot-Brocard group and found to be active against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Ferroquine, in combination with artefenomel, completed phase IIb clinical evaluation in 2019. More than 1000 studies have been published on ferrocenyl-containing pharmacophores against infectious diseases, including parasitic, bacterial, fungal, and viral infections, but the relationship between structure and biological activity has been scarcely demonstrated, unlike for ferrocifens and ferroquines. In a majority of ferrocene-containing drugs, however, the production of reactive oxygen species (ROS), in particular the OH. radical, produced by Fenton catalysis, plays a key role and is scrutinized in this mini-review, together with the supramolecular approach utilizing drug delivery nanosystems, such as micelles, metal-organic frameworks (MOFs), polymers, and dendrimers.

Application of Amyloid-Based Hybrid Membranes in Drug Delivery

The properties of amyloid fibrils, e.g., unique structural characteristics and superior biocompatibility, make them a promising vehicle for drug delivery. Here, carboxymethyl cellulose (CMC) and whey protein isolate amyloid fibril (WPI-AF) were used to synthesize amyloid-based hybrid membranes as vehicles for the delivery of cationic and hydrophobic drugs (e.g., methylene blue (MB) and riboflavin (RF)). The CMC/WPI-AF membranes were synthesized via chemical crosslinking coupled with phase inversion. The zeta potential and scanning electron microscopy results revealed a negative charge and a pleated surface microstructure with a high content of WPI-AF. FTIR analysis showed that the CMC and WPI-AF were cross-linked via glutaraldehyde and the interacting forces between membrane and MB or RF was found to be electrostatic interaction and hydrogen bonding, respectively. Next, the in vitro drug release from membranes was monitored using UV-vis spectrophotometry. Additionally, two empirical models were used to analyze the drug release data and relevant rate constant and parameters were determined accordingly. Moreover, our results indicated that in vitro drug release rates depended on the drug–matrix interactions and transport mechanism, which could be controlled by altering the WPI-AF content in membrane. This research provides an excellent example of utilizing two-dimensional amyloid-based materials for drug delivery.

Insight into the release mechanisms of diflunisal and salicylic acid from poly(vinyl alcohol). The role of hydrogen bonding interactions

Diflunisal (5-(2,4-Difluorophenyl)salicylic acid, DIF), salicylic acid (SAL) derivative, which, on the one hand, is active pharmaceutical ingredient, on the other hand, belongs to the compounds exhibiting excited-state intramolecular proton transfer (ESIPT) behaviour was used to study the drug interactions with poly(vinyl alcohol) (PVA) matrix. For clarifying the nature and mechanisms of the drug-matrix interactions the salicylic acid (SAL) molecule was selected as the model active ESIPT compound, whose physicochemical properties in different media are well understood. The solute-solvent interactions (non-specific (dipole-dipole) versus specific (hydrogen bonding)) of DIF and SAL with different neat solvents were investigated using the steady-state spectroscopic technique. The solvent effect on spectral behaviours of DIF and SAL was analyzed based on the parametric solvent scales. In order to identify functional groups in the PVA matrices, determine the structure present in the studied molecule-PVA system and thus obtain information about the potential interactions between PVA and the studied molecules, the Raman spectra of pure PVA, SAL-PVA and DIF-PVA systems were measured. It has been shown that the molecular structure of the active substance entrapped in the polymer matrix affects the structure of the polymer, i.e., isotactic (SAL-PVA) versus syndiotactic (DIF-PVA) structure. The analysis of drug release kinetics revealed that the DIF is more strongly bound to PVA in comparison to SAL, which confirms conclusions drawn from the analysis of the Raman spectra i.e., the isotactic structure of SAL-PVA material results in a faster initial release process of weakly bound, located on the surface of the polymer SAL molecules.

Alginate as a Promising Biopolymer in Drug Delivery and Wound Healing: A Review of the State-of-the-Art

Biopolymeric nanoparticulate systems hold favorable carrier properties for active delivery. The enhancement in the research interest in alginate formulations in biomedical and pharmaceutical research, owing to its biodegradable, biocompatible, and bioadhesive characteristics, reiterates its future use as an efficient drug delivery matrix. Alginates, obtained from natural sources, are the colloidal polysaccharide group, which are water-soluble, non-toxic, and non-irritant. These are linear copolymeric blocks of α-(1→4)-linked l-guluronic acid (G) and β-(1→4)-linked d-mannuronic acid (M) residues. Owing to the monosaccharide sequencing and the enzymatically governed reactions, alginates are well-known as an essential bio-polymer group for multifarious biomedical implementations. Additionally, alginate’s bio-adhesive property makes it significant in the pharmaceutical industry. Alginate has shown immense potential in wound healing and drug delivery applications to date because its gel-forming ability maintains the structural resemblance to the extracellular matrices in tissues and can be altered to perform numerous crucial functions. The initial section of this review will deliver a perception of the extraction source and alginate’s remarkable properties. Furthermore, we have aspired to discuss the current literature on alginate utilization as a biopolymeric carrier for drug delivery through numerous administration routes. Finally, the latest investigations on alginate composite utilization in wound healing are addressed.

Loading and Sustained Release of Pralidoxime Chloride from Swellable MIL-88B(Fe) and Its Therapeutic Performance on Mice Poisoned by Neurotoxic Agents

Maintaining a long-term continuous and stable reactivator blood concentration to treat organophosphorus nerve agent poisoning using acetylcholinesterase (AChE) reactivator pralidoxime chloride (2-PAM) is very important yet difficult. Because the flexible framework of MIL-88B(Fe) nanoparticles (NPs) can swell in polar solvents, pralidoxime chloride (2-PAM) was loaded in MIL-88B(Fe) NPs (size: ca. 500 nm) by stirring and incubation in deionized water to obtain 2-PAM@MIL-88B(Fe), which had a maximum drug loading capacity of 12.6 wt %. The as-prepared composite was characterized by IR, powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM), ζ-potential, Brunauer-Emmett-Teller (BET), and thermogravimetry/differential thermal analysis (TG/DTA). The results showed that under constant conditions, the maximum drug release rates of 2-PAM@MIL-88B(Fe) in absolute ethanol, phosphate-buffered saline (PBS) solution (pH = 7.4), and PBS solution (pH = 4) at 150 h were 51.7, 80.6, and 67.1%, respectively. This was because the composite showed different swelling behaviors in different solvents. In PBS solution with pH = 2, the 2-PAM@MIL-88B(Fe) framework collapsed after 53 h and released 100% of 2-PAM. For mice after intragastric poisoning with sarin (a neurotoxic agent), an atropine-assisted 2-PAM@MIL-88B(Fe) treatment experiment revealed that 2-PAM@MIL-88B(Fe) continuously released 2-PAM for more than 72 h so that poisoned AChE was continuously and steadily reactivated. The reactivation rate of AChE was 56.7% after 72 h. This composite is expected to provide a prolonged, stable therapeutic drug for the mid- and late-stage treatment of neurotoxic agent poisoning.

A Review of Sustained Drug Release Studies from Nanofiber Hydrogels

Polymer nanofibers have exceptionally high surface area. This is advantageous compared to bulk polymeric structures, as nanofibrils increase the area over which materials can be transported into and out of a system, via diffusion and active transport. On the other hand, since hydrogels possess a degree of flexibility very similar to natural tissue, due to their significant water content, hydrogels made from natural or biodegradable macromolecular systems can even be injectable into the human body. Due to unique interactions with water, hydrogel transport properties can be easily modified and tailored. As a result, combining nanofibers with hydrogels would truly advance biomedical applications of hydrogels, particularly in the area of sustained drug delivery. In fact, certain nanofiber networks can be transformed into hydrogels directly without the need for a hydrogel enclosure. This review discusses recent advances in the fabrication and application of biomedical nanofiber hydrogels with a strong emphasis on drug release. Most of the drug release studies and recent advances have so far focused on self-gelling nanofiber systems made from peptides or other natural proteins loaded with cancer drugs. Secondly, polysaccharide nanofiber hydrogels are being investigated, and thirdly, electrospun biodegradable polymer networks embedded in polysaccharide-based hydrogels are becoming increasingly popular. This review shows that a major outcome from these works is that nanofiber hydrogels can maintain drug release rates exceeding a few days, even extending into months, which is an extremely difficult task to achieve without the nanofiber texture. This review also demonstrates that some publications still lack careful rheological studies on nanofiber hydrogels; however, rheological properties of hydrogels can influence cell function, mechano-transduction, and cellular interactions such as growth, migration, adhesion, proliferation, differentiation, and morphology. Nanofiber hydrogel rheology becomes even more critical for 3D or 4D printable systems that should maintain sustained drug delivery rates.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

Connecting the dots in drug delivery: A tour d'horizon of chitosan-based nanocarriers system

One of the most promising pharmaceutical research areas is developing advanced delivery systems for controlled and sustained drug release. The drug delivery system (DDS) can be designed to strengthen the pharmacological and therapeutic characteristics of different medicines. Natural polymers have resolved numerous commencing hurdles, which hindered the clinical implementation of traditional DDS. The naturally derived polymers furnish various advantages such as biodegradability, biocompatibility, inexpensiveness, easy availability, and biologically identifiable moieties, which endorse cellular activity in contrast to synthetic polymers. Among them, chitosan has recently been in the spotlight for devising safe and efficient DDSs due to its superior properties such as minimal toxicity, bio-adhesion, stability, biodegradability, and biocompatibility. The primary amino group in chitosan shows exceptional qualities such as the rate of drug release, anti-microbial properties, the ability to cross-link with various polymers, and macrophage activation. This review intends to provide a glimpse into different practical utilization of chitosan as a drug carrier. The first segment of the review will give cognizance into the source of extraction and chitosan's remarkable properties. Further, we have endeavored to provide recent literature pertaining to chitosan applications in various drug delivery systems via different administration routes along with current patented chitosan formulations.

Release mechanisms and applications of drug delivery systems for extended-release

INTRODUCTION

Drug delivery systems with extended-release profiles are ideal in improving patient compliance with enhanced efficacy. To develop devices capable of a prolonged delivery kinetics, it is crucial to understand the various underlying mechanisms contributing to extended drug release and the impact thereof on modulating the long-term performance of such systems in a practical application environment.

AREAS COVERED

This review article intends to provide a comprehensive summary of release mechanisms in extended-release drug delivery systems, particularly polymer-based systems; however, other material types will also be mentioned. Selected current research in the delivery of small molecule drugs and macromolecules is highlighted. Emphasis is placed on the combined impact of different release mechanisms and drug properties on the long-term release kinetics in vitro and in vivo.

EXPERT OPINION

The development of drug delivery systems over an extended duration is promising but also challenging when considering the numerous interrelated delivery-related parameters. Achieving a well-controlled extended drug release requires advanced techniques to minimize burst release and lag phase, a better understanding of the dynamic interrelationship between drug properties and release profiles over time, and a thorough elucidation of the impact of multiple in vivo conditions to methodically evaluate the eventual clinical efficacy.

A Time-Programmed Release of Dual Drugs from an Implantable Trilayer Structured Fiber Device for Synergistic Treatment of Breast Cancer

Combination chemotherapy with time-programmed administration of multiple drugs is a promising method for cancer treatment. However, realizing time-programmed release of combined drugs from a single carrier is still a great challenge in enhanced cancer therapy. Here, an implantable trilayer structured fiber device is developed to achieve time-programmed release of combined drugs for synergistic treatment of breast cancer. The fiber device is prepared by a modified microfluidic-electrospinning technique. The glycerol solution containing chemotherapy agent doxorubicin (Dox) forms the internal periodic cavities of the fiber, and poly(l-lactic acid) and poly(ε-caprolactone) containing the angiogenesis inhibitor apatinib (Apa) form the double walls of the fiber. Rapid release of Dox can be obtained by adjusting the wall thickness of the cavities, meanwhile sustained release of Apa is achieved through the slow degradation of the fiber matrix. After the fiber device is implanted subcutaneously near to the implanted solid tumor of mice, an excellent synergistic therapeutic effect is achieved through time-programmed release of the combined dual drugs. The fiber device provides a platform to sequentially co-deliver dual or multiple drugs for enhanced combined therapeutic efficacy.

Composite Biopolymer-Based Wafer Dressings Loaded with Microbial Biosurfactants for Potential Application in Chronic Wounds

In this study two bioactive polysaccharide polymers kappa-carrageenan (CARR) and sodium alginate (SA) incorporated with microbial biosurfactants (BSs) were formulated as medicated wafer dressings for potential application in chronic wounds. Wafers were loaded with BSs at concentrations of 0.1% and 0.2% rhamnolipids (RL) and 0.1% and 5% sophorolipids (SL) and were functionally characterized using scanning electron microscopy (SEM), texture analysis (mechanical strength and in vitro wound adhesion), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD) and exudate handling properties (pore analysis, swelling index, water absorption (Aw), equilibrium water content (EWC), evaporative water loss (EWL) and water vapor transmission rate (WVTR). The wafers were tactile and ductile in appearance with a hardness range of 2.7⁻4.1 N and can withstand normal stresses but are also flexible to prevent damage to newly formed skin tissues. Wafers were porous (SEM) with pore sizes ranging from 78.8 to 141 µm, and BSs were not visible on the wafer surface or pore walls. The BSs enhanced the porosity of the wafers with values above 98%, while the Aw and EWC ranged from 2699⁻3569% and 96.58⁻98.00%, respectively. The EWL ranged from 85 to 86% after 24 h while the WVTR ranged from 2702⁻3080 g/m² day-1. The compatibility of BSs within the CARR-SA matrix was confirmed by seven characteristic functional groups which were consistently transmitted in the ATR-FTIR spectra. These novel medicated dressing prototypes can potentially help to achieve more rapid wound healing.

Controlled release technology for anti-angiogenesis treatment of posterior eye diseases: Current status and challenges

Antiangiogenic therapeutics, such as corticosteroids, VEGF targeting antibodies and aptamers have been demonstrated effective in controlling retinal and choroidal neovascularization related vision loss. However, to manage the chronic conditions, it requires long term and frequent intravitreal injections of these drugs, resulting in poor patient compliance and suboptimal treatment. In addition, emerging drugs such as tyrosine kinase inhibitors and siRNAs received much expectations, but the late stage clinical trials encountered various obstacles. Controlled release technology could improve the existing treatment regimen by extending therapeutic duration, reducing risks and burdens caused by frequent injections, and enabling new drugs to overcome the hurdles of translation. Here, we give qualitative and quantitative discussions about the principle mechanisms of polymeric reservoir, polymeric matrix and hydrogel systems. We also reveal the design rationales of the existing drug delivery and release systems in preclinical and clinical stages. Lastly, the animal models of ocular angiogenesis diseases are critically reviewed, which could help to facilitate the translation of controlled release technologies from bench to bedside.

Electromechanically Actuated Multifunctional Wireless Auxetic Device for Wound Management

The design and fabrication of a wound healing device for chronic wounds, with multiple functions for controlled drug delivery and exudate removal, has been described in this paper. The structural features have been machined and modified through laser cutting in a biocompatible polymer cast. Miniaturized versions of electronically actuated (lead-screw and pulley) mechanisms are used for the specific purpose of controlled drug delivery. These mechanisms have been studied and tested, being controlled through a microcontroller setup. An auxetic polymeric barrier membrane has been used for restricting the drug quantities administered. Drug delivery mechanisms are powered wirelessly, through an external, active RF component; this communicates with a passive component that is buried inside the wound healing device. The exudate removal efficiency of the device has been assessed through several simple tests using simulated wound exudate. It has been found that reasonably precise quantities of drug dosages to be administered to the wound site can be controlled through both drug delivery mechanisms; however, the lead-screw mechanism provides a better control of auxetic barrier membrane actuation and hence controlled drug delivery. We propose that this device can have potential clinical significance in controlled drug delivery and exudate removal in the management of chronic wounds.

Macro-scale model study of a tunable drug dispensation mechanism for controlled drug delivery in potential wound-healing applications

BACKGROUND

Auxetic materials tend to exhibit stretching in the direction of the applied load as well as in the perpendicular direction. This may be an inherent property of the material, or it might be a particular structural characteristic that confers it with auxetic properties. In this study, the auxetic properties of a rotating squares auxetic design were utilized in tandem with a stretching mechanism to manufacture a device that offers the advantages of adjustable pore size and hence tunable drug delivery characteristics.

METHODS

An auxetic polyurethane film was fabricated through the polymer casting technique. An acrylonitrile-butadiene-styrene (ABS) plastic mold for polymer casting was made through additive manufacturing. Stereolithography was used for fabrication of the mechanism that controlled pore size of the polymeric auxetic film. A laminate arrangement of the film and the mechanism was devised, through which movement of the mechanism controlled stretching of the auxetic film underneath.

RESULTS

Results were analyzed through image processing. It was observed that a 2-dimensional increase (in length and width) of the auxetic film took place that corresponded to an increase in pore size of the film. Several mathematical correlations were drawn up.

CONCLUSIONS

It may be concluded that the first factor controlling drug release kinetics is the pore size of the film. This study explored a prototype mechanism that has the potential for being used in devices for controlled drug delivery or in smart bandage systems that may enhance wound healing in chronic wound treatment.

In Vitro Evaluation of Poly-(ε-Caprolactone-Co-L-Lactide) Implants Containing Trypanocidal Drugs

Poly(e-caprolactone-co-L-lactide) copolyesters with different compositions were synthesized by bulk polymerization. The copolymers were characterized by NMR, GPC, and DSC analyses. Slow release devices were obtained as rods by extrusing polymer/drug mixtures (75/25, w/w) prepared by solution casting. The rods were coated by dipping in a methylene chloride solution of the core polymer. The in vitro release of isometamidium chloride (IMM) and ethidium bromide (EtBr), from these rods was carried out in phosphate buffer (PB) pH 7.4 at 3700. The release of IMM is faster than for EtBr. Initial IMM release is governed by osmotic pressure, whereas EtBr release is mainly diffusion controlled. The in vitro release of these drugs is governed by polymer matrix degradation at the later stage of the release process. The in vitro release of IMM from these copolymers depends on polymer composition and coating thickness. The in vitro release of EtBr may be controlled by polymer composition, polymer molecular weight, coating thickness, and device geometry.

Advanced Therapeutic Dressings for Effective Wound Healing--A Review

Advanced therapeutic dressings that take active part in wound healing to achieve rapid and complete healing of chronic wounds is of current research interest. There is a desire for novel strategies to achieve expeditious wound healing because of the enormous financial burden worldwide. This paper reviews the current state of wound healing and wound management products, with emphasis on the demand for more advanced forms of wound therapy and some of the current challenges and driving forces behind this demand. The paper reviews information mainly from peer-reviewed literature and other publicly available sources such as the US FDA. A major focus is the treatment of chronic wounds including amputations, diabetic and leg ulcers, pressure sores, and surgical and traumatic wounds (e.g., accidents and burns) where patient immunity is low and the risk of infections and complications are high. The main dressings include medicated moist dressings, tissue-engineered substitutes, biomaterials-based biological dressings, biological and naturally derived dressings, medicated sutures, and various combinations of the above classes. Finally, the review briefly discusses possible prospects of advanced wound healing including some of the emerging physical approaches such as hyperbaric oxygen, negative pressure wound therapy and laser wound healing, in routine clinical care.

Bolstering Components of the Immune Response Compromised by Prior Exposure to Adenovirus: Guided Formulation Development for a Nasal Ebola Vaccine

The severity and longevity of the current Ebola outbreak highlight the need for a fast-acting yet long-lasting vaccine for at-risk populations (medical personnel and rural villagers) where repeated prime-boost regimens are not feasible. While recombinant adenovirus (rAd)-based vaccines have conferred full protection against multiple strains of Ebola after a single immunization, their efficacy is impaired by pre-existing immunity (PEI) to adenovirus. To address this important issue, a panel of formulations was evaluated by an in vitro assay for their ability to protect rAd from neutralization. An amphiphilic polymer (F16, FW ∼39,000) significantly improved transgene expression in the presence of anti-Ad neutralizing antibodies (NAB) at concentrations of 5 times the 50% neutralizing dose (ND₅₀). In vivo performance of rAd in F16 was compared with unformulated virus, virus modified with poly(ethylene) glycol (PEG), and virus incorporated into poly(lactic-co-glycolic) acid (PLGA) polymeric beads. Histochemical analysis of lung tissue revealed that F16 promoted strong levels of transgene expression in naive mice and those that were exposed to adenovirus in the nasal cavity 28 days prior to immunization. Multiparameter flow cytometry revealed that F16 induced significantly more polyfunctional antigen-specific CD8⁺ T cells simultaneously producing IFN-γ, IL-2, and TNF-α than other test formulations. These effects were not compromised by PEI. Data from formulations that provided partial protection from challenge consistently identified specific immunological requirements necessary for protection. This approach may be useful for development of formulations for other vaccine platforms that also employ ubiquitous pathogens as carriers like the influenza virus.

Macroscale delivery systems for molecular and cellular payloads

Macroscale drug delivery (MDD) devices are engineered to exert spatiotemporal control over the presentation of a wide range of bioactive agents, including small molecules, proteins and cells. In contrast to systemically delivered drugs, MDD systems act as a depot of drug localized to the treatment site, which can increase drug effectiveness while reducing side effects and confer protection to labile drugs. In this Review, we highlight the key advantages of MDD systems, describe their mechanisms of spatiotemporal control and provide guidelines for the selection of carrier materials. We also discuss the combination of MDD technologies with classic medical devices to create multifunctional MDD devices that improve integration with host tissue, and the use of MDD technology in tissue-engineering strategies to direct cell behaviour. As our ever-expanding knowledge of human biology and disease provides new therapeutic targets that require precise control over their application, the importance of MDD devices in medicine is expected to increase.

Modeling mass transfer from carmustine-loaded polymeric implants for malignant gliomas

Significant advances in the encapsulation and release of drugs from degradable polymers have led to the Food and Drug Administration approval of Gliadel wafers for controlled local delivery of the chemotherapeutic drug carmustine to high-grade gliomas following surgical resection. Due to the localized nature of the delivery method, no pharmacokinetic measurements have been taken in humans. Rather, pharmacokinetic studies in animals and associated modeling have indicated the capability of carmustine to be delivered in high concentrations within millimeters from the implant site over approximately 5 days. Mathematical models have indicated that diffusion has a primary role in transport, which may be complemented by enhanced fluid convection from postsurgical edema in the initial 3 days following implantation. Carmustine's penetration distance is also presumably limited by its lipophilicity and permeability in the capillaries. This review discusses the mathematical models that have been used to predict the release and distribution of carmustine from a polymeric implant. These models provide a theoretical framework for greater understanding of systems for localized drug delivery while highlighting factors that should be considered in clinical applications. In effect, Gliadel wafers and similar drug delivery implants can be optimized with reduction in required time and resources with such a quantitative and integrative approach.

A Mechanistic Study of Wetting Superhydrophobic Porous 3D Meshes

Superhydrophobic, porous, 3D materials composed of poly( ε -caprolactone) (PCL) and the hydrophobic polymer dopant poly(glycerol monostearate- co- ε -caprolactone) (PGC-C18) are fabricated using the electrospinning technique. These 3D materials are distinct from 2D superhydrophobic surfaces, with maintenance of air at the surface as well as within the bulk of the material. These superhydrophobic materials float in water, and when held underwater and pressed, an air bubble is released and will rise to the surface. By changing the PGC-C18 doping concentration in the meshes and/or the fiber size from the micro- to nanoscale, the long-term stability of the entrapped air layer is controlled. The rate of water infiltration into the meshes, and the resulting displacement of the entrapped air, is quantitatively measured using X-ray computed tomography. The properties of the meshes are further probed using surfactants and solvents of different surface tensions. Finally, the application of hydraulic pressure is used to quantify the breakthrough pressure to wet the meshes. The tools for fabrication and analysis of these superhydrophobic materials as well as the ability to control the robustness of the entrapped air layer are highly desirable for a number of existing and emerging applications.

Mechanisms of monoclonal antibody stabilization and release from silk biomaterials

The availability of stabilization and sustained delivery systems for antibody therapeutics remains a major clinical challenge, despite the growing development of antibodies for a wide range of therapeutic applications due to their specificity and efficacy. A mechanistic understanding of protein-matrix interactions is critical for the development of such systems and is currently lacking as a mode to guide the field. We report mechanistic insight to address this need by using well-defined matrices based on silk gels, in combination with a monoclonal antibody. Variables including antibody loading, matrix density, charge interactions, hydrophobicity and water access were assessed to clarify mechanisms involved in the release of antibody from the biomaterial matrix. The results indicate that antibody release is primarily governed by hydrophobic interactions and hydration resistance, which are controlled by silk matrix chemistry, peptide domain distribution and protein density. Secondary ionic repulsions are also critical in antibody stabilization and release. Matrix modification by free methionine incorporation was found to be an effective strategy for mitigating encapsulation induced antibody oxidation. Additionally, these studies highlight a characterization approach to improve the understanding and development of other protein sustained delivery systems, with broad applicability to the rapidly developing monoclonal antibody field.

Effect of silk protein processing on drug delivery from silk films

Sericin removal from the core fibroin protein of silkworm silk is a critical first step in the use of silk for biomaterial-related applications, but degumming can affect silk biomaterial properties, including molecular weight, viscosity, diffusivity and degradation behavior. Increasing the degumming time (10, 30, 60, and 90 min) decreases the average molecular weight of silk protein in solution, silk solution viscosity, and silk film glass-transition temperature, and increases the rate of degradation of a silk film by protease. Model compounds spanning a range of physical-chemical properties generally show an inverse relationship between degumming time and release rate through a varied degumming time silk coating. Degumming provides a useful control point to manipulate silk's material properties.

3D superhydrophobic electrospun meshes as reinforcement materials for sustained local drug delivery against colorectal cancer cells

In this work we expand upon a recently reported local drug delivery device, where air is used as a degradable component of our material to control drug release (J. Am. Chem. Soc. 2012, 134, 2016-2019). We consider its potential use as a drug loaded strip to provide both mechanical stability to the anastomosis, and as a means to release drug locally over prolonged periods for prevention of locoregional recurrence in colorectal cancer. Specifically, we electrospun poly(ε-caprolactone) (PCL) with the hydrophobic polymer dopant poly(glycerol monostearate-co-ε-caprolactone) (PGC-C18) and used the resultant mesh to control the release of two anticancer drugs (CPT-11 and SN-38). The increase in mesh hydrophobicity with PGC-C18 addition slows drug release both by the traditional means of drug diffusion, as well as by increasing the stability of the entrapped air layer to delay drug release. We demonstrate that superhydrophobic meshes have mechanical properties appropriate for surgical buttressing of the anastomosis, permit non-invasive assessment of mesh location and documentation of drug release via ultrasound, and release chemotherapy over a prolonged period of time (>90 days) resulting in significant tumor cytotoxicity against a human colorectal cell line (HT-29).

Preparation of injectable auto-forming alginate gel containing simvastatin with amorphous calcium phosphate as a controlled release medium and their therapeutic effect in osteoporosis model rat

Highly soluble amorphous calcium phosphate powder (ACP) was added to the alginate gel as a buffering agent, in an attempt to enable widely controlled release while avoiding an acidification of the gel-environment. Therapeutic effects of the ACP-containing alginate gel which slowly releases a drug, simvastatin, on osteoporosis model rats were examined. A model drug, simvastatin, incorporated in the alginate gel with ACP up to 0.5%, was continuously released for a long time under the acidic condition. The release rate was controlled by the amount of ACP, serving as a buffer to suppress acidity. When the alginate solution intramuscularly injected in the rat, a soft gel was formed in the injected site. Simvastatin released from the gel containing 0.5% of ACP showed high therapeutic effect on osteoporosis rat. Thus, the present injectable long-sustained release system is expected to be a novel drug delivery controlling device.

The long-term potential of biodegradable poly(lactide-co-glycolide) microparticles as the next-generation vaccine adjuvant

Biodegradable polymeric microparticles of poly(lactide-co-glycolide) (PLG) have been extensively evaluated for drug delivery and vaccine applications over the last three decades. Despite a wealth of studies on the use of PLG microparticles in vaccines through controlled release of antigens, there is no commercial PLG-based vaccine as yet. The key challenge that prevented the development of PLG microparticles as commercial vaccines was the instability of encapsulated antigen. Over the years, advancements were made towards maintaining antigen integrity during PLG microparticle preparation and sterilization. In parallel and independently, development of PLG microparticles as therapeutic commercial products established PLG with an excellent safety record in humans, and as a suitable candidate for next-generation vaccines. Through the combination of Toll-like receptor agonist encapsulation and surface adsorption of antigen, PLG microparticles can be used as a vaccine adjuvant to address unmet medical needs, such as vaccines against HIV, malaria and TB. With strategic development of PLG-based vaccines, PLG microparticles can offer advantages over the conventional vaccine adjuvants allowing commercial development of this adjuvant.